C language decimal to binary display gadget implementation code

Calculator in the display of binary digits, if the beginning is 0. Will not be displayed, for people in the SCM mix, this is sometimes very troublesome, so write a small tool.

The function is to enter the decimal number, and then display the 2, every 4 Spaces, can adjust the number range (multiple of 8)

If anyone can know the calculator similar to win7 under Linux, please reply and inform. Thank you very much ~

Such as:

$dec2bin 1, 135
Num 8 Binary is: 0B1000 0111
Done!
= = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =

$dec2bin 2, 135
Num 16 Binary is: 0B0000 0000 1000 0111
Done!
= = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =

The code is as follows:

= = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =

#include <stdio.h>
#include <stdlib.h>
#define HALF_CHAR 4
void bit_print(int bit_num, int a);
int main(int argc, char **argv)
{
    if (argc != 3) {
        printf("use: name num decn");
        exit(1);
    }

    bit_print(atoi(argv[1]),atoi(argv[2]));
    printf("done!n");
    return 0;
}
void bit_print(int bit_num, int a)
{
    int i;
    int n = sizeof(char) * 8 * bit_num;
    int mask = 1 << (n - 1);
    printf("Num %d Binary is : 0B", (bit_num * 8));
    for (i = 1; i <= n; ++i) {
        putchar(((a & mask) == 0) ? '0' : '1');
        a <<= 1;
        if (i % HALF_CHAR == 0 && i < n)
            putchar(' ');
    }
    putchar('n');
}